This question, despite its simpleness is actually quite complicated with the answer requiring a lot more factors to consider. Traditionally, the radar detector needs to be put to the windshield where its front view is not obstructed. But with the development of better police radar/laser speed guns, radar detectors evolved into more sophisticated devices which requires specific installation guidelines. So depending on the model, the brand and its capability, the most ideal place to put your radar detector would vary.

Moreover, current laws and road restrictions also dictates where you would place your radar detector. If you're driving in a place or state that considers this kind of technology as illegal then flaunting it on the dashboard or below the windshield is a totally bad idea. Besides the fact that you could get fined and have your detector confiscated when you are caught, placing your radar detector unit away from the police's eyes increases your chances of not getting a ticket.

Let's say a police officer caught you of speeding. According to police interviews, an officer is most likely let you off with a warning if you have been caught speeding. They will think that you just got carried away and would believe that you will be more careful the next time around. However, if they do see a radar detector on your dashboard or anywhere else in visible sight, they will see this as proof that your intention was to go beyond the speed limit and have installed such a device to avoid being caught.

This reason alone makes it more appropriate to install the device away. One way of accomplishing that is to mount the radar antenna of the detector behind the front grill and the Visual Display Unit (VDU) inside the driver compartment or below the radio. Other models or units may need to be disassembled in order to access the antenna and split them apart.

Unfortunately, some data detectors are required to be place high above the windshield. These data detectors are of laser types, the added elevation is probably needed to detect better laser speed guns by the police.

Unlike radars where radio transmission travel in waves, laser beams are narrower and can be blocked by practically anything that goes between it the beams. Whereas, in the case of radars, the waves or radar beams penetrate glass, plastic, cardboard and even the human body.

The next option that you have it to place it on an area where you can get it removed quickly and hide away in case you get caught by the police.